1. Field of the Invention
The present invention relates to a method for treating a surface of aluminum material and a plasma treating apparatus using such material, and particularly to a method for treating a surface of aluminum material contacting corrosion gas and a plasma treating apparatus using aluminum material whose surface is treated.
2. Description of the Related Art
A plasma treating apparatus has been used in an etching process, which is one of the manufacturing processes of a semiconductor device. As a plasma treating apparatus, there is a parallel plate type plasma treating apparatus comprising a mount electrode on which a treating object is mounted and an opposite electrode provided to be opposite to the mount electrode.
By use of such a plasma treating apparatus, the following plasma etching of a treating object is performed. More specifically, the treating object is mounted on a surface of the mount electrode. In this state, high-frequency power is applied onto the mount electrode and/or the opposite electrode to generate plasma between these electrodes. In plasma, components of etching gas are dissociated, and an active radical is generated. The surface of the treating object is etched by the active radical.
As an electrode material in the above-mentioned plasma treating apparatus, high-purity aluminum containing a little amount of impurity material is suitably used. However, such high-purity aluminum is expensive. Moreover, since mechanical strength of high-purity aluminum is low, high-purity aluminum is easily broken in processing high-purity aluminum as an electrode. Due to this, in order to overcome the economical reason and ensure the mechanical strength necessary for processing, aluminum containing a certain degree of impurity material, e.g., impurity material of 2 to 3 wt %, has been used as electrode material. Moreover, for the same reason, aluminum material containing a small amount of impurity material has been used in other materials of the plasma treating apparatus such as a chamber. As impurity materials contained in such aluminum, for example, heavy metals such as iron, chrome, nickel, copper, etc. are included.
The electrode and the chamber, which are formed of such aluminum containing impurity material (hereinafter called as aluminum material), are etched during plasma etching. Particles or the atom of aluminum and the impurity material are dispersed into the chamber by etching. These particles or the atoms are mixed with a thin film formed in the treating object such as a semiconductor wafer, and the so-called heavy metal contamination may be caused.
In order to solve this problem, in conventional, anodic oxidation is provided on the surface of aluminum, and the surface of aluminum is coated with an alumite coating film. The alumite coating film has resistance to corrosion, and high hardness as compared with aluminum. Whereby, etching of the aluminum material in the plasma etching treatment is controlled to prevent particles or the atom of aluminum and the impurity material from being splashed from the aluminum material.
However, the alumite coating film, as such, is slightly etched by plasma etching. Therefore, there is a case in which the alumite coating film is etched in the plasma treatment and the material contained in the alumite coating film is splashed into the chamber. As a result, even if the alumite coating film is formed on the surface of the aluminum material the generation of heavy metal contamination of the treating object cannot be completely prevented.
Conventionally, carbon tetrachloride (CCl.sub.4) gas is mainly used in etching, for example, polycrystalic silicone. However, since CCl.sub.4 gas has strong toxicity, and environmental pollution is considered, the use of CCl.sub.4 is regulated. Due to this, in place of CCl.sub.4 gas, there is a tendency to use mixing gas of hydrogen bromine (HBr)/hydrogen chloride (HCl).
HBr/HCl gas has higher corrosive than CCl.sub.4. Due to this, the alumite coating film, which is formed on the surface of the aluminum material, is more etched with Br/HCl gas as compared with the case of using CCl.sub.4 gas. Therefore, the incidence of the particles, the atom or the like of aluminum and the impurity material, which are dispersed from the alumite coating film, in the case of the plasma etching treatment using HBr/HCl gas is higher than the case of the plasma etching treatment using CCl.sub.4. Due to this, the heavy metal contamination of the treating object may be easily generated.
Moreover, the alumite coating film takes in moisture, etc. when being formed by anodizing aluminum. When a inside of the chamber is made various, in which the aluminum material is placed, the water or the like in the alumite coating film are discharged into atmosphere in the chamber. This phenomenon is called as "outgas". If outgas is occurred, vacuum degree in the chamber of the plasma treating apparatus or concentration of process gas, or the component is changed. As a result, there occurs a case in which a desired plasma generation condition cannot be obtained and even treatment cannot be provided onto the surface of the treating object. In order to prevent generation of gas from the alumite coating film, the aluminum material, which is formed on the surface of the alumite coating film, is conventionally baked to generate gas compulsorily. However, since a clack is generated on the alumite coating film by the generation of gas, the alumite coating film is peeled off, and the particles of alumite are generated, such a treatment is unfavorable.